Photographic products, processes and compositions



May 28, 1963 M. GREEN ETAL PHOTOGRAPHIC PRODUCTS, PROCESSES ANDCOMPOSITIONS Filed Dec. 21, 1959 l0 SUPPORT I I -PHOTOSENSITIVE LAYERPROCESSING COMPOSITION l3 lMAGE-REcElvlNfi LAYER I4 "SUPPORT SPREADERSHEET I2 SSING COMPOSITION ll PHOTOSENSITIVE LAYER IMAGE-RECEIVING LAYERI4 SUPPORT FIGZ M .INVENTORJ m 6M EM ATTORNEYS 3,091,530 PHOTOGRAPHICPRODUCTS, PROCESSES AND COMPOSITIONS Milton Green, Newton Highlands,Meroe M. Morse, Boston, and Myron S. Simon, Newton Center, Mass.,assignors to Polaroid Corporation, (Zarnbridge, Mass, a corporation ofDelaware Filed Dec. 21, 1959, Ser. No. 361,127 3 Claims. (Cl. 96-=-29)The present invention relates to photography and more particularly tocompositions, products, and processes useful in the development ofselectively photoexposed photosensitive silver halide elements, andespecially to compositions and products useful in diffusion transferprocesses, particularly in high speed diffusion processes Wherein asilver halide photosensitive emulsion has been underexposed in relationto its A.S.A. exposure index, that is, to processes for deriving usefulphotographic transfer prints from latent images formed at low exposurelevels.

In diffusion transfer processes, for the formation of positive silverimages, a latent image contained in a selectively photoexposedphotosensitive silver halide emulsion is developed. Almost concurrentlytherewith a soluble silver complex is obtained by reaction of a silverhalide solvent with the unexposed and undeveloped silver halide of saidemulsion. Preferably, the photosensitive silver halide emulsion isdeveloped with a processing composition in a viscous condition which isspread between the photosensitive element comprising the silver halideemulsion, and a print-receiving element comprising, preferably, asuitable silver precipitating layer. The processing composition effectsdevelopment of the latent image in the emulsion and substantiallycontemporaneous therewith forms a soluble silver complex, for example, athiosulfate or thiocyanate complex, with undeveloped silver halide. Thissoluble silver complex is, at least in part, transported in thedirection of the print-receiving element and the silver thereof islargely precipitated in the silver precipitating layer of said elementto form the desired positive image therein.

High speed diffusion transfer processes are generally of the type inWhich, for example, a silver halide stratum containing a latent imageformed at a low exposure level and an image-receiving stratum, insuperposition, are subjected to a processing composition containing ahighly energetic silver halide developing agent and a silver halidesolvent in order to form a silver transfer print in and/ or on theimage-receiving stratum. The silver halide developing agent serves toreduce photoexposed silver halide to silver in the photosensitiveemulsion stratum. The silver halide solvent reacts with unreduced silverhalide, to form the aforementioned soluble silver complex which, inturn, is reduced in the presence of the image-receiving stratum to formthe desired positive print. The photosensitive stratum may besubsequently dissociated from the image-receiving stratum. In accordancewith a preferred embodiment of the present invention, the silver halidestratum may be underexposed in relation to its rated A.S.A. exposureindex and the silver halide developing agent is specifically selectedfrom the class hereinafter set forth.

Preferably, the image-receiving stratum is in such condition as to causesilver reduced there, in comparison with silver reduced in thephotosensitive silver halide stratum, to possess very high coveringpower, that is, opacity per given mass of reduced silver. This highcovering power is achieved by accumulating the silver deposited in theggt silver-receptive stratum in unusually dense masses, for example, byminimizing the thickness of the stratum in which the silver-receptivematerial is contained.

The high speed diffusion transfer processes set forth herein providereadily available and uniquely simple processes for producingsatisfactory high quality of good resolunch and trivial granularity atlow illumination levels, for example, at overall exposures that areequivalent to A.S.A. exposure indices of 600 and up.

Accordingly, objects of the present invention are to provide: novelproducts, developer composition, and processes employing such productsand developer compositions, for the development of selectivelyphotoexposed silver halide emulsions; novel products and developercompositions useful in high speed diffusion transfer processes wherein aselectively photoexposed silver halide emulsion has been substantiallyunderexposed in relation I to its A.S.A. exposure index; and to employ,in processes of the aforementioned type, a silver halide developingagent selected from the class hereinafter set forth.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the several steps and the relationand order of one or more of such steps with respect to each of theothers, and the products and compositions possessing the features,properties and the relation of elements which are exemplified in thefollowing detailed disclosure, and the scope of the application of whichwill be indicated in the claims.

For a fuller understanding of the nature and objects of the presentinvention, reference should be had to the following detailed descriptiontaken in conjunction with the accompanying drawing wherein:

FIGURE 1 is a diagrammatic enlarged cross-sectional View illustratingthe association of elements during one stage of the performance of adiffusion transfer process, for the production of positive silverprints, the thickness of the various materials being exaggerated; and

FIG. 2 is a view similar to that of FIGURE 1 illustrating theassociation of elements during one stage of the performance of anotherdiffusion transfer process, for the production of positive silverprints. i

Amidol (2,4-diaminophenol hydrochloride) is an energetic silver halidedeveloping agent which has received only limited use in generalphotography due to its rapid oxidation in solution. On the other hand,amidol may be employed in diffusion transfer processes by incorporatingit in a rupturable container which is substantially airtight. It hasbeen found, however, that use of amidol in diffusion transfer processesgives rise to a deeply colored oxidation product which will stain thehands and clothes of the person performing the transfer process.

This deeply colored oxidation product apparently is formed after theprocessing composition has been spread between the photosensitive andimage-receiving elements. The layer of processing, compositionpreferentially adheres to the developed photosensitive element, and willstain objects, e.g., hands or clothes, with which it comes into contact.

It has been found that the silver halide developing agents of thisinvention possess many of the desirable properties of amidol but do notgive rise to highly colored oxidation products in diffusion transferprocesses. These new silver halide developing agents also aresubstantially more stable than amidol when employed in tray or tankprocessing in general photography.

'The novel class of silver halide developing agents of the presentinvention may b? represented by the formula:

( OH H wherein either R or R comprises a benzyl group, or ahydroxybenzyl group, and the remaining R or R is hydrogen; and thenuclear substituted halogen derivatives, preferably the nuclearsubstituted chlorine derivatives thereof.

The developing agents of the present invention may be employed in theform of their acid addition salts, such as the hydrochloride.Thefollowing compounds are examples of silver halide developing agentswithin the scope of the present invention:

mac -Q 4-amino-2benzylamino-phenol 2-amino-4-benzy1amino-pheno14-amino-2- (m-hydroxybenzylamino) phenol NHa I IHCHF-Q 2-a1nino-4-(m-hydroxybenzylamino) -phenol 2-amino-4 (p-hydroxybenzylamino -phenol;

4-a1nino 6-chloro-2- p-hydroxybenzylamino) -phenol A preferred method ofpreparing the compounds of Formula A comprises reacting either ano-amino-p-nitrophenol or a p-amino-o-nitro-phenol with eitherbenzaldehyde or hydroxybenzaldehyde and efiecting reduction of theresultant product, for example, by hydrogenation in the presence of asuitable catalyst such as palladium on barium sulfate.

The last-mentioned synthetic procedure is further illustrated inconjunction with the following specific examples which set outrepresentative applications of the synthetic procedure.

EXAMPLE 1 Synthesis of 4-Amino-2-Benzylamin0-Phenol In a 250 cc.Erlenmeyer flask were placed 15.4 grams of 2-amino-4-nitro-phenol and10.6 grams of benzaldehyde. The mixture reacted almost immediately.(Hydroxybenzaldehydes require heating to effect reaction.) The product,2-(N-benzylidene-amino) 4-nitro-phenol, was crystallized from alcoholand dried. The product melted at 196 to 198 C. [Yield 94.5%.]

A mixture comprising 12.1 grams of the Schiff base product, 6 grams of5% palladium on barium sulfate, and 200 cc. of ethyl acetate washydrogenated in a Parr shaker bottle at an initial pressure ofapproximately 35 pounds per square inch. The bottle was shaken until thetheoretical amount of hydrogen Was absorbed (20 to 30 minutes). Themixture was then filtered through a Celite (trade name of Iohns-ManvilleSales Corp., New York, N.Y., for diatomaceous-earth filtration aids) padinto concentrated hydrochloric acid. The product, 4-amino-2-benzylamino-phenol, a white solid, precipitated spontaneouslyfrom the acid solution as the hydrochloride. The precipitate wasseparated by filtration, washed with ether anddried in a vacuumdesiccator over potassium hydroxide. [Yield 89.2%.]

EXAMPLE 2 Synthesis of 2-Amin0-4-Benzylamin0-Phen0l4-amino-2-nitro-phenol was reacted withbenzaldehyde to provide4-(N-benzylidene-amino)-2-nitro-phenol, melting point 104 to 105 C.,which then was reduced to provide the desired product, according to theprocedures of Example 1.

EXAMPLE 3 Synthesis of 4-Amin0-2-(p-Hydroxybenzylamino)-Phen0l EXAMPLE 4Synthesis of 4-Amin0-2-(m-Hydr0xybenzylamin0)- I Phenol2-amino-4-nitro-phenol was reacted with m-hydroxybenzaldehyde to provide2-(N-[m-hydroxybenzylidene]- amino)-4-nitro-phenol, melting point 197 to200 C., which in turn was reduced to provide the desired product,according to the procedures of Example 1.

EXAMPLE Synthesis of 2-Amin0-4-(m-Hydroxybenzylamino)- Phenol4-amino-2-nitro-phenol was reacted with m-hydroxybenzaldehyde to provide4-(N-[m-hydroXybenzylidene} amino)-2-nitro-phenol, melting point 158 to168 C., which in turn was reduced to provide the desired product,according to the procedures of Example 1.

EXAMPLE 6 Synthesis of 2-Amin0-4-(p-Hydroxybenzylarnino)-Phen0l4-amino-2-nitro-phenol was reacted with p-hydroxybenzaldehyde to provide4-(N-[p-hydroxybenzylidene]- amino)-2-nitro-phenol, melting point 188 to193 C., which in turn was reduced to provide the desired product,according to the procedures of Example 1.

EXAMPLE 7 Synthesis of 4-Amino-6-Chloro-2-(p-Hydroxybenzylamino -Ph enolZ-amino-6-chloro-4-nitro-phenol was reacted with p-hydroxybenzaldehydeto provide 6-chloro-2-(N-[p-hydroxybenzylidene] amino)-4-nitro-phcnol,melting point 235 to 237 C., which in turn was reduced to provide thedesired product, according to the procedures of Example 1.

The novel silver halide developing agents of the present invention areuseful in conventional black-and-white development and in diffusiontransfer processes, both dye and silver. Examples of such processes aredisclosed in U.S. Patents Nos. 2,543,181 and 2,662,822 to Edwin H. Land.

In particular, the novel silver halide developing agents of the presentinvention are highly useful in so-called high speed diffusion transferprocesses wherein high quality silver transfer prints are obtained froma silver halide emulsion which has been substantially underexposed inrelation to its A.S.A. rating. Such an exposure provides a latent imagehaving a density gradient confined to the low exposure or toe region ofthe negative materials characteristic curve. Processes of this type aredisclosed in the copending application of Edwin H. Land et al., SerialNo. 564,492, filed February 9, 1956.

The speed of a photosensitive material comp-rises generally anempirically derived relative measurement which may be defined as a valuerepresenting the reciprocal of the exposure required to produce a givenresult. Any precise definition of speed, therefore, is based upon theselection of a particular result as the standard reference point. Aprecise quantitative measure of speed has been developed from the workof L. A. Jones et al., as reported in Mees, The Theory of thePhotographic Process, the Macmillan Company, New York, 1944, ChaptersXIX and XXII. This work suggested a system in which negative sensitivematerials are assigned a speed that is in terms of the exposure requiredto give a negative image from which a positive print of specifiedquality can be produced.

Based on this work, The American Standards Association, Incorporated,has established standards for rating sensitive materials for speed.Under such standards, emulsion speed is considered as a value inverselyproportional to the minimum exposure which must be incident upon thenegative material, from the scene element of minimum brightness in whichdetail is visible, in order that a print of excellent quality can bemade from the resultant negative. These standards specify techniques forplotting the characteristic H. and D. curve of a negative material, thatis, the curve relating the logarithm of the original exposure of thenegative to density in said negative. The value of speed derived fromthe standard characteristic curve so determined is specified as equal tothe reciprocal of the exposure E, on the characteristic curve at whichthe slope is 0.3 times the average slope for a log exposure range of 1.5of which E is the minimum exposure. The precise method for determiningspeed in this manner is described in detail in the publication of TheAmerican Standards Association, Inconporated, PH 2.51954, and titledAmerican Standard Method for Determining Photographic Speed and ExposureIndex.

The A.S.A. speed rating is to be distinguished from What is termed theA.S.A. exposure index, for use with exposure meters and calculators. TheA.S.A. exposure index is determined by the formula: A.S.A. exposureindex=S.A.S. speed/4. The exposure index so obtained indicates generallythe correct exposure rating to which an A.S.A. calibrated exposure metermust be set in order that it give correct exposure data for producingpictures of satisfactory high quality.

The ASA speed rating is to be further distinguished from what may betermed diffusion transfer process exposure index. In'suoh processes, theexposure index may be based on a curve relating original exposure of thenegative to the density in the resultant positive. It has been foundexperimentally that the diffusion transfer exposure index of a silvertransfer process may be determined by plotting a characteristic curve ofthe reflection density of the positive as a function of the log exposureof the negative, determining the exposure in meter-candleseconds(m.c.s.) at the point on this curve corresponding to a density of 0.50,and dividing the constant, 4.0, by the exposure so determined. Theexposure index so obtained indicates generally the correct exposurerating of a silver transfer process to which an exposure meter,calibrated to the A.S.A. exposure index, must be set in order that itgive correct exposure data for producing transfer prints of satisfactoryhigh quality, and is sometimes referred to as the equivalent A.S.A.exposure index.

Both the A.S.A. exposure index and the diffusion transfer exposure indexcan "be judged or rated according to sensitometric criteria withexposure, that is, the luminance flux reaching a unit :area of thephotosensitive surface, being measured inm.c.s. The equivalence of theforegoing methods of determining rated A.S.A. exposure indices anddiffusion transfer exposure indices can be readily established byobtaining a standardized silver transfer positive and determining theillumination, by measuring with an exposure meter calibrated accordingto an A.S.A. standard which includes a computer in which has beenentered the shutter duration and f-stop of the camera, found necessaryto provide the standard transfer print.

In the subsequent discussion, the term A.S.A. exposure index is intendedto signify the exposure index determined in accordance with theaforementioned American Standards Association specifications. The termdiffusion transfer exposure index is intended to signify, in referenceto diffusion transfer processes, or the materials used therein, theexposure index as determined in the aforementioned manner. Bothdesignations, in one sense, serve the same purpose. The A.S.A. exposureindex of the negative is based upon the exposure to which the negativemust be subjected in order to obtain a good photograph of apredetermined subject by conventional processing, whereas the diffusiontransfer exposure index is based upon the exposure to which a negativefor use in a silver diffusion transfer process must be subjected inorder to obtain a good positive by that process. Both, therefore, aredirect guides to the exposure setting which must be made in a camera inorder to obtain proper exposure. Nevertheless, the two definitions ofexposure must be carefully distinguished from each other because,although the A.S.A. exposure index is related qualitatively to theproduction of a positive of high quality, it is a term which describesthe character of a negative material. This negative material,nevertheless, may be employed, for example, in a silver diffusiontransfer process of the present invention to effect a diffusion transferexposure index vastly different from the A.S.A. exposure index of thenegative material. In the novel diffusion transfer processes of thepresent invention, a positive print of satisfactory high quality isproduced from a negative material subjected to exposures less, in somecases many times less, than recommended by its rated A.S.A. exposureindex. Such an exposure provides a latent image having a densitygradient confined to the low exposure or toe region of the negativematerials characteristic curve.

Referring now to the drawing, FIGURE 1 illustrates one assemblage andprocess of the present invention in the performance of a diffusiontransfer process for the production of positive silver prints. Asdepicted in the drawing, an aqueous allkaline fi-uid layer 12 of asilver halide developing agent chosen in accordance with the presentinvention and a suitable silver halide solvent are spread betweenphotosensitive emulsion layer 11 which is superposed on support It) andimage receiving layer 13 which is aflixed to support layer 14.Image-receiving layer 13 preferably contains silver precipitating agentsor nuclei such as the silver precipitating nuclei disclosed in U.S.Patent No. 2,698,237. Support layer 14 may comprise an opaque materialwhere a reflection print is desired or may comprise a transparentmaterial Where a transparency is desired.

Fluid layer 12 may be obtained by distribution of the processingcomposition in a substantially uniform manner between photosensitiveemulsion layer .11 and imagereceiving layer =13, for example, inaccordance with the procedures disclosed in U.S. Patent No. 2,543,181.For example, one or more rupturable containers may be attached to eitherphotosensitive emulsion layer 11 and/ or image-receiving layer 13 suchthat upon superpostiion of the respective layers 11 and 13 saidcontainer or containers are so positioned as to be capable, uponrupture, of releasing their contents in a substantially uniform layerbetween and in contact with the opposed surface of each of said layers.Rupture of the container or containers and spreading of the contentsthereof may be accomplished, for example, by compression between a pairof opposed, suitably gapped, rollers.

For clarity, the particular developer selected, the degree to which thephotosensitive layer is exposed, and the character of thesilver-receptive layer will be described in detail hereinafter.

The processing composition preferably comprises a film-forming transferprocessing composition. It may comprise, for example, one or more of thepreviously enumerated developing agents of the present invention, analkali such as sodium hydroxide, a silver halide complexing agent suchas sodium thiosulfate, and a high molecular weight film-formingthickening agent such as sodium carboxymethyl cellulose. All thesematerials are preferably in aqueous solution. These photographic agentsare preferably contained in solution in the processing composition priorto the spreading thereof as layer 12, but they may be in part or inwhole added to the processing composition as it is spread between thephotosensitive emulsion 11 and image-receiving layer 13, said agentsbeing so located on, in, or adjacent to a surface of one or both of saidlayers as to be dissolved by or otherwise interacted with the liquidagent when the latter wets said layers.

In carrying out the aforementioned transfer process, the photosensitiveemulsion 11 is exposed to a predetermined subject matter to form thereina latent image of said subject matter. The exposed emulsion issuperposed on image-receiving layer 13 and the photographic processingcomposition 12 spread between the opposed surfaces of said emulsion 11and said image-receiving layer 13. Reagents permeate into thephotosensitive emulsion 11, developing the latent image containedtherein and forming a soluble silver complex of unexposed silver halide.Soluble silver complex is transported from photosensitive emulsion layer11, at least in part,by imbibition, to printreceiving stratum 13' andthe silver of the complex is precipitated thereon and/or therein toprovide the desired positive image formation. The laminate formed by thespreading of the processing composition as layer 12 betweenphotosensitive emulsion layer 11 and print-receiv ing layer 13 is keptintact for approximately /2 to 1 /2 minutes, preferably 1 minute, and atthe termination of this time interval the print-receiving layer 13 isdissociated from photosensitive emulsion 11 as, for example, by manualstripping.

A further transfer process of the present invention for the productionof positive silver prints is illustrated in FIG. .2 and comprises aspreader sheet 15, a layer of relatively viscous processing composition12, a photosensitive gelatin emulsion layer 11 superposed onimagereceiving layer 13 which is, in turn, superposed on a support layer14. As stated in connection with the description of FIGURE 1,image-receiving layer 13 preferably contains silver precipitating nucleiand support layer 14 may comprise either an opaque or transparentmaterial.

Fluid composition layer 12 may be obtained by spreading a photographicprocessing composition, for example, in a manner disclosed in U.S.Patent No. 2,698,244. As disclosed in the aforementioned patent, theliquid processing composition may be disposed in a rupturable containerso positioned in regard to the appropriate surface of photosensitiveemulsion layer 11 that, upon compression by spreader sheet 15, asubstantially uniform layer 12 of processing composition is distributedover the external surface of said photosensitive emulsion 11, withrespect to image-receiving layer 13.

In carrying out the last-mentioned transfer process, the photosensitiveemulsion 11 is exposed to a predetermined subject matter to form thereina latent image of said subject matter. A substantially uniformdistribution of processing composition 12 is distributed on the externalsurface of said emulsion 11, as for example, according to the previouslydescribed procedure. Processing composition reagents permeate intophotosensitive emulsion '12, developing the latent image containedtherein according to the point-to-point degree of exposure thereof.Substantially contemporaneous with the development of the latent image,an imagewise distribution of soluble silver complex is formed fromunexposed and undeveloped silver halide within said emulsion. At leastpart of said silver complex, solubilized, is transferred, by imbibition,to print-receiving stratum 13. The transferred silver complexes arereacted therein to provide a positive, reversed image of the latentimage. Subsequent to formation of the positive image in image-receivinglayer 13, dissociation of said layer from emulsion layer 11 may beeffected.

Where desired, the image-receiving layer 13 may be dissociated fromemulsion layer 11 by stripping the emulsron from the surface thereof. Aconventional stripping layer may be provided to facilitate separation ofemulsron layer 11 from image-receiving layer 13 subsequent to transferprocessing. Sufficient abrasion-resistant properties may be provided toimage-receiving layer 13 as to alleviate anynecessity of subsequentlyovercoating the external surface of said image-receiving layer 13 with atransparent abrasion-resistant water-soluble plastic to preventsubsequent laceration and resultant degradation of the positlve image.Image-receiving layer 13 may also comprise sufficient integraldimensional stability as to alleviate the necessity of a separatesupport layer 14.

In the last-mentioned processes, spreading of the liquidprocessingcomposition on the external surface of photosensitive emulsion layer 11is preferably effected by rup ture of a suitably positioned frangiblecontainer and dis tribution of its processing composition contents bymeans of a converted cellulose acetate spreader sheet, that is, acellulose acetate sheet the surface of which has been converted tocellulose. When employed, the converted cellulose acetate spreader sheetmay exhibit an adhesive capacity for the processing composition inexcess of the adhesive capacity exhibited by the photosensitiveernulsion. A means is thus provided for effecting dissociation of theprocessing composition from contact with the photosensitive emulsion,subsequent to image formation, by dissociating the spreader sheet fromits proximate relationship to the external emulsion surface.

It will be apparent that the facility with which the photosensitiveemulsion layer is dissociated from contact with the print-receivinglayer may be increased by providing a conventional stripping layerinterposed between said emulsion and said print-receiving layer. Thestripping layer may be coated on the surface of the print-receivingelement and a photosensitive emulsion thereafter coated on the externalsurface of said stripping layer.

While distribution of the processing composition in diffusion transferprocesses has been described utilizing a frangible container, it will beapparent that said container provides a convenient means of distributingthe liquid processing composition to permit the processing to beeffected within a suitable camera apparatus. The diffusion transferprocesses of this invention may be otherwise effected. For example, aphotosensitive element, after exposing a suitable apparatus and Whilepreventing further exposure thereafter to actinic radiation, may beremoved from such apparatus and permeated with the liquid processingcomposition as, for example, by coating, spraying, flowing etc., thecomposition on said photosensitive element or otherwise wetting saidele: ment with a composition, following which the permeated, exposed,photosensitive element, still without additional exposure to actinicradiation, is brought into contact with the image-receiving element forimage formation in the manner heretofore described.

The rupturable containers may be constructed in accordance with thedisclosures set forth in U.S. Patent No. 2,634,886. Containers of thistype are generally constructed from a blank comprising a flexible,deformable, three-ply sheet material comprising, respectively, an outerlayer of kraft paper, a layer of metal foil and an inner layer or linerof a thermoplastic resin. The container blank is folded upon itself suchas to provide a fluid-containing cavity and a container exhibiting asealed passage adjacent to an edge thereof which may be substantiallyuniformly unsealed throughout a predetermined length of the seal passageupon application of stress to the container. The passage may be formedby the utilization of differential adhesion.

As previously noted, the print-receiving stratum preferably containssilver precipitating agents or nuclei, whose presence during thetransfer process has a desirable efiect on the amount and character ofthe silver precipitated during positive print formation. Examples ofsuch silver precipitating agents are the metallic sulfides andselenides, thiooxalates, and the thioacetarnides, and colloidal metalsdisclosed in U.S. Patent No. 2,698,237. It is also desirable, asdisclosed in that patent, to provide, as the vehicle for the silverprecipitating agents, a macroscopically continuous film that consists ofsubmacroscopic agglomerates of minute particles of a suitablewater-insoluble, inorganic, preferably siliceous, material such assilica aerogel. The use of such a vehicle for the precipitating agentstends to aggregate the silver that is precipitated into its mosteffective condition for print formation.

Silver halide solvents suitable for incorporation in the processingcomposition include conventional fixing agents such as sodiumthiosulfate, sodium thiocyanate, ammonium thiosulfate, or associationsof cyclic imides and hitrogeneous bases such as associations ofbarbiturates or uracils and ammonia or amines. Of these, theconventional fixing agents specified are preferred. Preferably, thesolution also contains a film-forming material such as a water-solubleplastic, starch or gum imparting a viscosity of from 1000 to 200,000centipoises at a temperature of 10 20 C. in order to permit the solutionto be readily con trolled during and after spreading.

It will be apparent that the relative proportions of the agents of thedeveloper composition set forth herein may be altered to suit therequirements of the operator. Thus, it is Within the scope of thisinvention to modify the herein described developing compositions by thesubstitution of preservatives, alkalies, silver halide solvents, etc.,other than those specifically mentioned. When desirable, it is alsocontemplated to include, in the developing composition, components suchas restrainers, accelerators, etc. Similarly, the concentration ofdeveloping agent may be varied over a wide range and when desirable thedeveloping agent may be disposed in the photosensitive element prior tothe exposure of the emulsion. The developing agent may be disposed in aseparate permeable layer of the photosensitive element and/or in thephotosensitive emulsion.

The emulsion support layer designated in the drawing as 10 may compriseany of the various types of conventional rigid or flexible supports, forexample, glass, paper, metal, and polymeric films of both the synthetictypes and those derived from naturally occurring products.

The photosensitive emulsion stratum may comprise a commerciallyavailable silver halide gelatin emulsion such as sold by Eastman KodakCompany under the trade names Microfile, Spectrum Analysis, ContrastProcess, S X X Aero Recon, Ve-richrome, Royal Pan, Royal X Pan, or Tri XPan, or sold by E. I. du Pont under the trade names Fine Grain Pan, HighSpeed Pan, Arrow Pan, or Superior 3, or sold by Ansco under the tradename Triple S Pan, or sold by Gevaert under the trade name Gevapan.

Of the developing agents of the present invention, compounds whereineither R or R comprises a hydroxybenzyl group possess specific andunexpected advantages. These compounds are characterized by unexpectedlyhigher process speeds when employed in diffusion transfer processes. Thehigher process speeds may be the result of a solubilizing effectimparted to the developer molecule by the hydroxyl group substituted onthe benzyl group.

The compounds of the present invention may also be used in smallquantities with other silver halide developers, for example,hydroquinone or one of its derivatives, to produce high speed prints ofexceptional quality by diffusion transfer processes.

The present invention will be illustrated in greater detail inconjunction with the following specific examples which set outrepresentative useof the novel silver halide devel oping agents .of thisinvention in high speed diffusion transfer processes, which however arenot limited to the details therein set forth and are intended to beillustrative only.

The indicated developing agents employed and the results obtained in thespecific examples are hereinafter set forth in tabular form. (Specificexamples employing metol, amidol and hydroquinone, respectively, havebeen reported for the purpose of providing comparative data.)

A silver iodobromide emulsion having the designated A.S.A. exposureindex is exposed to a predetermined subject through a stop which givesrise to the indicated diffusion transfer exposure index, advanced insuperposed relationship with an image-receiving element, comprising asilver-receptive stratum containing silver precipitating nucleidisperse-d in a matrix of colloidal silica coated on a water-imperviousbase according to the practice described in US. Patent No. 2,823,122,issued to Edwin H. Land on February 11, 1958, between a pair ofpressure-applying rollers to spread a processing composition comprising:

Water cc 398 Carboxymethyl cellulose (high viscosity) grams- 15.25Sodium sulfite do 25.6 Sodium hydroxide do 15.2 Sodium thiosulfate do5.4

6-nitrobenzimidazole 2 do 0.5

1 1 and a concentration of the specified developer designated in thefollowing table, between the photoexposed emulsion and theimage-receiving element in a thin layer approximately 0.003 of an inchthick. After an imbibition period of approximately 60 seconds, theemulsion, together with 12 can be obtained only from an emulsion thathas been sufiiciently exposed within the range of exposures specifiedfor the emulsion. Underexposed emulsions result in a negative havingonly an image from which it is impractical to obtain a satisfactoryprint by conventional the layer of processing composmon, 1s stnpped fromthe processes. image-receiving element to uncover the positive print,The present mvention obviates the problem of conwhlch providedsatisfactory contrast, denslty and range. structmg a satisfactorynegative from an underexposed Concentration Imbibi- Density DensityDiffusion Emulsion Shoulder Compound (grams/ tion (maxi- (mini- SlopeTransfer A.S.A. Speed cc. process- Tune mum) mum) Exposure Exposure(m.s.c.)

mg com- (mmutes) Index Index position) 0. 4 1 1. 40 0.01 2. 02 2, 000200 0.00040 0. 4 1 0.82 0. 01 0. 90 0, 000 ca. 800 0. 00022 0. 4 1 1. 070.01 1. 18 109 200 0. 0030 0. 4 1 1. 31 0. 03 0. 90 180 ca. 800 0. 00240. 4 1 1. 07 0. 03 1. 38 1, 420 200 0. 00035 0.4 1 1. 43 0. 00 1. 24 7,520 ca. 800 0. 00009 0. 4 2 1. 00 0. 0. 42 072 200 0. 00078 0.2 2 1.580.20 2.10 1,120 200 0 00074 0.2 2 1.00 0.02 0. 84 10,000 ca. 200 0 0001s0. 4 1 1. 38 0. 00 1.14 8,800 021.800 0. 000080 0. 4 1 1.08 0. 00 0. 705, s40 ca. 800 0. 00011 0. 4 1 1. 00 0. 0e 0. 66 s, 400 ca. 800 0.000080 0. 4 2 1. 10 0. 01 1. 34 1, 840 200 0. 00064 *Proccssingcomposition contains an additional 1% sodium thiosulfate.

possessing an A.S.A. exposure index of 200 are coated on a transparentfilm base; the spercprcsents the A.S.A. exposure index designated by theemulsion manufacturer. The emulsions possessing an A.S.A. exposure indexof ca. 800 are coated on the external surface of arefiecting layer whichis on a paper base; the A.S.A. exposure index ca. 800 was determinedexperimentally.

The chief function of a photographic negative material as used inpictorial photography is to reproduce as density differences theluminance differences existing in the object photographed. The minimumuseful exposure will, therefore, be that required to reproduce theminimum difference existing in the shadow regions of the object by meansof some minimum density difierence in the resulting image.

When the novel developing agents of this invention are used in highspeed diffusion transfer processes, the region of the A.S.A.characteristic curve of the negative used in accordance with the presentinvention lies at a relatively low exposure level and corresponds to anexposure gradient predominantly below approximately 0.015 m.c.s.Ordinarily, the fog level in such a case is at a point on thecharacteristic curve that corresponds to an exposure gradientpredominantly above approximately 0.005 m.c.s.

As used herein and in the .above table, the shoulder speed is theminimum amount of exposure in motorcandle-seconds which can be used toexpose the negative emulsion and give a transfer image in which there isthe minimum contrast which the eye can distinguish, i.e., there isvisible detail in the shadow regions of the transfer image. Thisexposure level is determined at the point on the shoulder portion of thepreviously described characteristic curve of the positive transfer imagewhere the slope is 0.4.

As illustrated in the aforementioned specific examples thephotosensitive emulsions of the present processes are underexposed inrelation to their respective A.S.A. exposure index to produce therein aweak latent imagehaving an exposure gradient predominantly in the toeregion of the A.S.A. density versus log exposure curve of thephotosensitive emulsion. The emulsion is therefore exposed to produce alatent image lying in the toe region of the A.S.A. characteristic curvefor the negative emulsion such that, by the standard A.S.A. developmentmethod, it would be impractical to develop the emulsion such as toprovide a useful conventional negative image. By means of thecompositions, products and processes of the present invention, one mayadvantageously employ a photosensitive emulsion having a stated A.S.A.exposure index and provide said emulsion with an effective exposure thatordinarily would require a photosensitive emulsion having a higherA.S.A. exposure index to provide an acceptable positive print resultanttherefrom.

With conventional developing practices, good negatives emulsion, forexample, by intensification, hypersensitiz-ation, latensificationtechniques, so as to obtain a satisfactory positive print. In addition,the present invention provides satisfactory positive images from bothunderexposed and adequately exposed conventional silver halidephotosensitive emulsions. As previously mentioned, a convenient measureof the amplification of image development, obtained according to thepresent disclosure, over the results obtained from conventionaldevelopment practices, is in terms of increase in the speed or quantumexcitation sensitivity of the emulsion as indicated by the resultspreviously set forth, over the normal specified speed of the sameemulsion as determined by the results of standard development practice.

Since certain changes may be made in the above products, processes andcompositions without departing from the scope of the invention hereininvolved, it is intended that all matter contained in the abovedescription or shown in the accompanying drawing shall be interpreted asillustrative and not in a limiting sense.

What is claimed is:

1. A photographic process which comprises the steps of underexposing aphotosensitive silver halide emulsion with respect to its A.S.A.exposure index to produce therein a latent image having an exposuregradient in the toe region of the A.S.A. density versus log exposurecurve of said silver halide emulsion; developing said emulsion with anaqueous alkaline solution of a silver halide developing agent of theformula:

wherein one of R and R is a hydroxybenzyl group, and the other of R andR is hydrogen, and the diaminophenol nuclear substituted halogenderivatives thereof; contacting unexposed and undeveloped silver halidetherein with a silver halide solvent to form an imagewise distributionof soluble silver complex; transferring at least part of said imagewisedistribution, by imbibition, to a superposed image-receiving materialcontaining a silver precipitating agent; and there precipitatingtransferred soluble silver complex to provide a silver print of fullpictorial density to said image-receiving material.

2. A process as defined in claim 1, wherein said developing agent is 4amino-2-(p-hydroxybenzylamino)- phenol.

3. A process as defined in claim 1, wherein said developing agent is4-amin0-2-(rn-hydroxybenzylamino)- phenol.

4. A process as defined in claim 1, wherein said developing agent is2-amino-4-(m-hydroxybenzylamino)- phenol.

5. A process as defined in claim 1, wherein said developing agent is2-amino-4-(p-hydroxybenzylamino)- phenol.

:6. A process as defined in claim 1, wherein said developing agent is4-.amino-6-chloro-2-(p-hydroxybenzylamino) -phenol.

7. A photographic process which comprises the steps of exposing aphotosensitive gelatino silver halide emulsion with a luminance fluxincident thereon not in excess of about 0.015 imeter-candle-second;developing exposed silver halide in said photosensitive emulsion with anaqueous alkaline solution containing a silver halide developing agent ofthe formula:

wherein one of R and R is a hydroxybenzyl group, and the other of R andR is hydrogen, and the diaminophenol nuclear substituted chlorinederivatives thereof; and a silver halide solvent; contacting unexposedand undeveloped silver halide therein with said silver halide solventand forming thereby an imagewise distribution of a soluble silvercomplex in unexposed areas of said emulsion, as a function of thepoint-to-point degree of exposure thereof; transferring from saidemulsion, at least in part, by imbibition, said imagewise distributionof soluble silver complex to a print-receiving layer, containing silverprecipitating nuclei, in superposed relationship, with said emulsion;and there precipitating silver complex to provide thereby a reversed,positive, full scale silver print of the latent image.

8. A photographic process which comprises the steps of exposing aphotosensitive gelatino silver halide emulsion with a light fluxincident thereon predominantly with- 14 in the exposure range delineatedby the toe region of said emulsions characteristic H. and D. curve,determined according to A.S.A. standard PH 2.5-1954; developing exposedsilver halide in said photosensitive emulsion with an aqueous alkalinesolution of a silver halide developing agent of the formula:

wherein one of R and R is a hydroxybenzyl group, and the other of R andR is hydrogen, and the diaminophenol nuclear substituted chlorinederivatives thereof; contacting undeveloped silver halide with a silverhalide solvent and forming thereby an imaginewise distribution ofsoluble silver complex in the unexposed areas of said emulsion;transferring, =by imbibition, from said emulsion, at least in part, saidimaginewise distribution of soluble silver complex to a print-receivingelement, containing silver precipitating agents, in superposedrelationship With said emulsion; and precipitating said silver complexto provide thereby a reversed, positive print possessing acharacteristic curve with a slope greater than the slope of said H. andD. curve, said positive prints characteristic curve determined byplotting a reflection density of the positive print as a function of thelog exposure of the negative.

References Cited in the file of this patent UNITED STATES PATENTS516,754 Brack Mar. 20, 1894 2,543,181 Land Feb. 27, 1951 2,740,717 Yutzyet al Apr. 3, 1956 2,837,497 Delmonte June 3, 1958 FOREIGN PATENTS20,050 Great Britain Sept. 7, 1908 OTHER REFERENCES The AmateurPhotographer and Photography, January 7, 1925, p. 7.

Clerc: Photographic Theory and Practice, 2d Ed., Pitman and Sons,London, 1937, page 253.

Mees: The Theory of the Photographic Process, Rev. Ed, Macmillan Co.,New York, 1954, pages 552-53.

Glafkides: Photographic Chemistry, 1, Fountain Press, London (1958),page 125.

1. A PHOTOGRAPHIC PROCESS WHICH COMPRISES THE STEPS UNDEREXPOSING APHOTOSENSITIVE SILDER HALIDE EMULSON WITH RESPECT TO ITS A.S.A. EXPOSUREINDEX TO PR~DUCE THEREIN A LATENT IMAGE HAVING AN EXPOSURE GRADIENT INTHE TOE REGION OF THE A.S.A. DENSITY VERSUS LOG EXPOSURE CURVE OF SAIDSOLVER HALIDE EMULSION; DEVELOPING SAID EMULSION WITH AN AQUEOUSALKALINE SOLUTION OF A SILVER HALIDE DEVELOPING AGENT OF THE FORMULA: